update some sslproxy host files to use variables. This will allow nginx to start even if the upstream is not ready

dockerfiles/services/sslproxy/hosts/jenkins.xai-corp.net.conf

@@ -3,6 +3,11 @@ proxy_cache_path /data/nginx/cache/jenkins levels=1:2 keys_zone=jenkins:10m max_
 
 # jenkins.xai-corp.net
 server {
+    # this is the internal Docker DNS, cache only for 30s
+    resolver 127.0.0.11 valid=30s;
+
+    set $backend http://dkhost.xai-corp.net:8080;
+
     listen  443 ssl;
     server_name jenkins.xai-corp.net;
     ssl_certificate     /etc/letsencrypt/live/xai-corp.net/fullchain.pem;
@@ -18,7 +23,7 @@ server {
         proxy_set_header        X-Forwarded-Host $host;
         proxy_set_header        X-Forwarded-Proto $scheme;
 
-        proxy_pass http://dkhost.xai-corp.net:8080;
+        proxy_pass $backend;
     }
 
 }